Rapid-deployment portal monitors employing visible light imaging and gamma ray imaging has been proposed. For example, K. Ziock, “The Use of Gamma-Ray Imaging to Improve Portal Monitor Performance,” 2007 IEEE Nuclear Science Symposium Conference, pp. 1198-1208 (2007) discloses simultaneous monitoring of multiple lanes of traffic from the side of a roadway. A roadside tracker may employ automated target acquisition and tracking software to identify and track vehicles in visible light images.
In this setup, the field of view of a visible light camera is calibrated to the field of view of a high energy radiation imager. The high energy radiation imager “harvests” the gamma ray data specific to each vehicle, integrating its radiation signature for the entire time that is in the field of view of the high energy radiation imager. Thus, vehicle-specific radiation signature may be generated while avoiding source confusion problems that plague non-imaging approaches to the problem of deterring unlawful transportation of radioactive materials.
Typically, the high energy radiation imager and the visible light camera in such a system have significantly different installation locations. Typically, the light visible light camera is installed above the height of vehicles to overlook the passing vehicles to capture as many features of passing vehicles as possible. The bulky high energy radiation imager is typically installed at the height of the passing vehicles to maximize the capture of radiation signals. Because of the different geometry employed for the two types of imagers, cross-calibration between the two types of imagers poses a difficulty. However, a highly accurate correlation between the pixel coordinates of the high energy radiation imager and the visible light camera is required in such a scenario to accurately track moving vehicles that potentially carry radioactive materials.
In view of the above and other reasons, there exists a need for a method for accurately determining the correlation between the high energy radiation imager pixel coordinates and the visible light camera pixel correlations.